Freezing Bacteria-Liquid N2 OK?

Hello All,
I was wondering about the feasability of storing frozen bacterial stocks
under liquid nitrogen vs. storing at -80oC. Are the cells viable? Should
they first be frozen slowly prior to storing under liquid nitrogen? Or is
snap freezing them okay? Should they be frozen as glycerol stocks-or is
DMSO or DMF okay to use instead? I have always in the past stored them at
-80oC (in glycerol or with DMSO).
I appreciate any and all responses-thanks in advance.
Kimberly Baldwin
kbal at med.pitt.edu
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Kimberly Baldwin
kb44+ at andrew.cmu.edu